ScientiaHorticulturae, 32 {1987) 67-72 67 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Influence of Temperature, KNO3, GA3 and Seed Drying on Emergence of Papaya Seedlings

SHELDON C. FURUTANI

College of Agriculture, University of Hawaii at Hilo, Hilo, HI (U.S.A.)

MIKE A. NAGAO

Hawaii Agricultural Experiment Station, University of Hawaii, Hilo, HI (U.S.A.)

(Accepted for publication 24 December 1986)

ABSTRACT

Furutani, S.C. and Nagao, M.A., 1987. Influence of temperature, KN03, GA3 and seed drying on emergence of papaya seedlings. Scientia Hortic., 32: 67-72.

Papaya (Caricapapaya L.) seeds soaked in potassium nitrate (KN03) or gibberellic acid (GA3) for 15 min exhibited an increased percentage emergence and a reduced time for 50% seedling emergence in comparison to seeds soaked in H20. Sowing seeds in pots and heating to 35 °C had higher percentage seedling emergence than heating to 25 ° C. Soaking seeds in KN03 or GA3 before or after drying for 2 weeks did not alter the KN03 or GA3 effects. Plants grown from KNO3-treated seeds appeared normal, whereas plants grown from GA3-treated seeds had elongated hypocotyls.

Keywords: Carica papaya L.; drying; gibberellic acid; potassium nitrate; seedling emergence; temperature.

INTRODUCTION

Germination of papaya ( Caricapapaya L. ) seeds is slow and sporadic ( Perez et al., 1980), but is improved by removing the sarcotesta prior to planting ( Gherardi and Valio, 1976; Perez et al., 1980; Reyes et al., 1980 ) or soaking in gibberellic acid (GA3) ( Yahiro and Oryoji, 1980; Nagao and Furutani, 1986). Reyes et al. (1980) isolated inhibitors in the sarcotesta and inner seed coat but not in the embryo and endosperm.

Soaking in KNO3 (Hashimoto, 1961; Ells, 1963; Perez et al., 1980) or GA3 (Hashimoto, 1961; Yahiro and Oryoji, 1980; Nagao and Furutani, 1986) or sowing seeds at elevated temperatures (Yahiro, 1979) have been shown to improve the uniformity of seedling emergence and percentage emergence of several crop species. This study was undertaken to evaluate the effect of ele- vated temperatures and varying concentrations of KNO3 and GA3 on papaya

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seedling emergence, and to determine whether emergence is affected when seeds are treated before or after drying.

MATERIALS AND METHODS

For all experiments, seeds of cultivar 'Kapoho Solo' were collected from ripe, freshly picked fruits that were grown in the Hilo area. Seeds were cleaned ( sarcotesta removed), washed with distilled water and blotted dry with paper towels prior to treatment. Seeds were planted 0.5 cm deep in 15.5-cm standard plastic pots containing moistened No. 2 grade vermiculite, and seedling emerg- ence was scored as positive when hypocotyls extended above the surface of the media. Emergence was recorded daily after the seeds were sown.

K N 0 3 , GA3 and heated-bed treatments . - Freshly cleaned seeds were soaked in aqueous solutions of GA3 at 0.0, 0.6, 1.2 or 1.8 mM, or in KNO3 at 0.0, 0.5 or 1.0 M for 15 min prior to sowing. The 15 min soaking time was utilized since preliminary experiments showed that 15-, 30-, 45- and 60-min soaks were not significantly different. The seeds were sown into pots and were placed either on heated (35 + 5 ° C) or non-heated (25 + 5 ° C ) benches (temperature was maintained by thermostatically controlled electric propagation mats) in a fiberglass greenhouse and seedling emergence was recorded daily for 21 days.

K vs. NO3 treatments . - Cleaned papaya seeds were soaked in distilled water, 1.0 M KN03, CaNO3, KC1 or CaC12 solutions for 15 min. The seeds were planted and grown on non-heated (25 + 5 ° C ) benches under greenhouse conditions as described above. Seedling emergence was recorded on a daily basis for 35 days.

Chemical t r ea tmen t before and after seed drying. - Seeds were soaked for 15 rain in either 1.6 mM GA3, 1.0 M KNO3 or distilled water immediately after cleaning or following drying for 2 weeks at 22 ° C and 50% RH. Seeds were sown in pots and grown on heated (35 + 5 ° C ) benches as described above. Seedling height and percentage seedling emergence were recorded at 30 days after planting.

Statistical analysis. - All experiments were arranged as randomized complete block designs and consisted of 4 replicates of 50 seeds/replicate. Values for percentage seedling emergence and time to 50% seedling emergence (Orchard, 1977) were analyzed by analysis of variance and means were separated by LSD. Percentage values were transformed by the square-root transformation and tested for homogeneity of variance before analysis. Values from Experiment 1 were analyzed by standard error (SE) .

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TABLE I

The effect of media temperature and soaking seeds in gibberellic acid (GA3) or potassium nitrate (KN03) on seedling emergence of papaya

Chemical dip Percentage seedling emergence Days to 50% seedling (15 rain ) emergence concentration

Temperature ofmedia (°C) Temperature ofmedia (°C)

25 35 25 35

GA (raM) 0.0 6 14 30 26 0.6 21 21 22 21 1.2 32 40 22 18 1.8 33 44 19 15

KN03 (M) 0.0 5 14 31 26 0.5 34 48 20 16 1.0 49 56 17 14

SE ± 3.2 ± 3.3 __+ 1.0 ± 0.9

RESULTS

E x p e r i m e n t 1. K N 0 3 , GA3 and heated-bed treatments. - Percentage seedling emergence was greater for KNO3- and GA3-treated seeds when compared to seeds soaked in distilled water ( Table I) . Increasing the KNO3 concentrat ion from 0 to 1.0 M and GA3 from 0 to 1.8 m M increased percentage seedling emergence 9.8- and 5.5-fold over the controls at 25 ° C; at 35 °C emergence was increased 4.0- and 3.1-fold, respectively. Seeds t reated with KN03 had a higher overall percentage seedling emergence than GA3 t reatments at both tempera- tures. Also, percentage seedling emergence at 35 °C was significantly higher (significant F t e s t , P- -0 .01 ) than at 25°C after 21 days.

Days to 50% seedling emergence decreased with increasing concentrat ions of KNO3 and GA3 ( Table I ). Seeds t reated with 1.8 mM GA3 and 1.0 M KNO3 reached 50% seedling emergence 11-14 days earlier at 25°C and 11-12 days earlier at 35 ° C compared to disti l led-water-treated seeds.

E x p e r i m e n t 2. K os. NO3 treatment . - Seeds soaked in KN03 and CAN03 had the highest percentage seedling emergence and the shortest t ime to 50% seed- ling emergence (Table II) . KC1 t rea tment also increased the percentage of seedlings emerging and reduced the emergence time, but was not as effective as the K N 0 3 and CAN03 soaking treatments . There was no difference between control and CaCl2-soaked seeds for percentage seedling emergence.

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TABLE II

The effect of soaking papaya seeds in potassium nitrate (KN03), potassium chloride (KC1), calcium nitrate (CAN03) or calcium chloride (CaC12) solution or distilled water (H20) on seed- ling emergence

Chemical treatment Percentage Days to 50% (15 min soaking) seedling emergence seedling emergence

1.0 M KN03 77 15.8 1.0 M KCI 34 23.4 1.0 M CaNO3 73 18.6 1.0 M CaC12 10 39.0 H20 (control) 7 28.4

L.S.D. (P= 0.05) 11 5.1

Experiment 3. Chemical treatment before and after seed drying. - Percentage seedling emergence with KNOs and GAs was consistantly higher whether soak- ing t rea tments were applied before or after seed drying (Table III) . When seeds were dried for 2 weeks prior to t reatment , percentage seedling emergence in the GAs and distilled-water t rea tments increased to 82 and 17% from 71 and 7%, respectively. No effect from drying was evident in the KNO3 treatments.

Days to 50% seedling emergence was less for KNO3- and GAs-treated seeds compared to the controls (Table III) . When t rea tment was applied before the 2-week drying period, seedlings from GAs-treated seeds emerged faster than from KNOs-t rea ted seeds. However, there was no difference between GAs and KNO3 when the seeds were t reated at 2 weeks after drying.

Seedling heights at 30 days after planting were consistently greater for GAs-

TABLE III

The effect of soaking papaya seeds in potassium nitrate (KN03) or gibberellic acid (GA3) solu- tions before and after drying for 2 weeks on seedling emergence

Chemical treatment (15 rain Percentage Days to 50% soaking) seedling emergence seedling emergence

Seeds treated before 2 weeks' drying 1.0 M KN03 72 15.9 1.6 mM GAs 71 11.7 H20 (control) 7 24.8

Seeds treated after 2 weeks' drying 1.0 M KNO~ 78 15.4 1.6 mM GAs 82 13.5 H20 (control) 17 26.2

L.S.D. (P=0.05) 7 2.5

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treated seeds ( 4.8 cm ) than seedlings from KN03 ( 3.4 cm ) and H20 ( 3.1 cm) treatments. Increased seedling height from the GA3 treatment was the result of abnormal hypocotyl elongation. The KNO3-treated seeds were greener and more vigorous than the other treatments.

DISCUSSION

Soaking seeds in KNO3 or GA3 solutions prior to planting and sowing seeds in pots on heated beds produced rapid emergence of seedlings. Potassium nitrate is well documented as a compound which increases the germination of photo- dormant seeds (Roberts, 1973). Hashimoto (1961) reported that tobacco seeds exhibited enhanced germination with nitrate solution. Addition of gibberellin to the nitrate solution was synergistic in promoting germination (Hashimoto, 1961). Currently, the International Seed Testing Association (ISTA, 1976) recommends using KNO3 to overcome dormancy of many light-requiring seeds.

Papaya seeds are not reported to be light-requiring. However, they respond to the KNO3 treatment. In our experiments, seeds responded similarly to KNO3 and CAN03. Seeds did not respond to CaC12 treatment and exhibited only a minimal response to KC1. Thus, the stimulation of germination by KNO3 appears to be in response to nitrate.

GA3 also enhanced emergence of papaya seeds as effectively as the KNO3 treatment, and this is in agreement with reports by other workers (Yahiro and Oryoji, 1980). The response to GA3 suggests that poor germination may involve a dormancy mechanism that is overcome by GA3 treatment (Khan, 1981 ).

An important observation from this study is the persistence of the KN03 and GA3 treatments. Treatments remain effective when applied before or after a 2-week drying period.

REFERENCES

Ells, J.E., 1963. The influence of treating tomato seeds with nutrient solution on emergence rate and seedling growth. Am. Soc. Hortic. Sci., 83: 684-687.

Gherardi, E. and Valio, I.F.M., 1976. Occurrence of promoting and inhibitory substances in the seed arils of Caricapapaya L. J. Hortic. Sci., 51: 1-4.

Hashimoto, T., 1961. Influence of inorganic nitrogenous compounds on tobacco seed germination induced by gibberellin GA3, kinetin and ammonium salts of organic acids. Plant Cell Physiol., 2: 463-469.

International Seed Testing Association, 1976. International rules for seed testing. Seed Sci. Tech- nol., 4: 1-7.

Khan, A.A., 1981. Hormonal regulation of primary and secondary seed dormancy. Israel J. Bot., 29: 207-224.

Nagao, M.A. and Furutani, S.C., 1986. Improving germination of papaya seed by density separa- tion, potassium nitrate and gibberellic acid. HortScience, 21: 1439-1440.

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Orchard, T.J., 1977. Estimating the parameters of plant seedling emergence. Seed. Sci. Technol., 5: 61-69.

Perez, A., Reyes, M.N., and Cuevas, J., 1980. Germination of two papaya varieties: effect of seed aeration, K-treatment, removal and sarcotesta, high temperature, soaking in distilled water, and age of seed. J. Agric. Univ. Puerto Rico 64: 173-180.

Reyes, M.N., Perez, A. and Cuevas, J., 1980. Detecting endogenous growth regulators on the sar- cotesta, endosperm, and embryo by paper chromotography on fresh and old seeds of two papaya varieties. J. Agric. Univ. Puerto Rico, 64: 164-172.

Roberts, E.H., 1973. Oxidative processes and the control of seed germination. In: Seed Ecology. Butterworths, London, pp. 189-218.

Yahiro, M., 1979. Effects of seed-pretreatment on the promotion of germination in Papaya, Carica papaya L. Mem. Fac. Agric. Kagoshima Univ., 15: 49-54.

Yahiro, M. and Oryoji, Y., 1980. Effects of gibberellin and cytokinin treatments on the promotion of germination in papaya, Caria papaya L., seeds. Mem. Fac. Agric. Kagoshima Univ., 16: 45-51.